When you click on any highlight icon in Google hotel listings an overlay is triggered with more details about hotel features and you can swipe to see more highlights, or expand more photos and review.

Depending on the highlight Google can either let you know that a particular amenity is a rare find for hotels in the selected area or give it a rating from 1 to 5, which seems to be the average of all user reviews mentioning the highlight.

Also, Google can show relevant photos and reviews (sourced from different sites).